A drive unit of an information instrument uses an optical pickup for using in CD, CD-R, DVD and the like, in which a semiconductor laser device having an optimum laser emission wavelength and an optimum luminous energy depending on a recording medium to be used is incorporated.
In general, an optical pickup comprises a semiconductor laser device having an incorporated semiconductor laser element, in which one semiconductor laser chip (hereinafter referred to as “LD chip”) is die-bonded on one sub-mount so that an axis of a light emitted from the LD chip directs in a predetermined direction relative to the sub-mount. In addition, there is an optical pickup comprising a plurality of optical sources each having the same wavelength and optical output in order to enhance a speed of the pickup.
Further, there is a semiconductor laser device incorporating a semiconductor laser element formed by die-bonding one LD chip emitting lights with different wavelengths on one sub-mount. However, in this case, an angle difference between axes of the lights from two optical sources is unchanged by changing die-bonding conditions.
Since an optimum laser emission wavelength and an optimum laser emission intensity depend on a recording medium to be used, when it is required to use different recording media in one information instrument, for example, two optical pickups are incorporated in a drive unit of the information instrument, or two semiconductor laser devices are incorporated in one optical pickup, resulting in making an optical system complicated and in enlarging the whole information instrument.
In addition, even when the semiconductor laser device comprises a semiconductor laser element having an LD chip emitting lights with different wavelengths, a large difference in an optical output between recording to and reading from a recording medium is required. It is difficult to fabricate a plurality of optical sources, whose laser wavelengths and optical outputs differ greatly from each other, within one LD chip.
According to the present invention, an optical pickup having a plurality of optical sources whose emission wavelengths and optical outputs differ from each other can be easily produced by using a semiconductor laser device having a semiconductor laser element capable of emitting a plurality of lights with different wavelengths incorporated therein, said semiconductor laser element being formed by die-bonding on one sub-mount a plurality of LD chips having emission wavelengths and optical outputs suitable for different recording media.
FIG. 1 shows a schematic perspective view of a semiconductor laser element 1 in which on a sub-mount 101, one red LD chip 102 and one infrared LD chip 103 are mounted, as an example of a semiconductor laser element formed by die-bonding the plurality of LD chips described above on one sub-mount. In addition, FIG. 2 shows a schematic perspective view of an optical pickup 2, which is produced by using a semiconductor laser device 21 having the above semiconductor laser element 1 incorporated therein. The semiconductor laser device 21 comprises mainly a stem 201 and a lead wire 202, and the semiconductor laser element 1 is incorporated in a tip of the stem 201.
In the optical pickup 2 having the above features, as shown in FIG. 3, it is desired that both an emitted light axis 106 of the red LD chip 102 and an emitted light axis 107 of the infrared LD chip 103 are in an acceptable prescribed angular range (108 and 109) relative to a predetermined reference axis 203. The predetermined reference axis 203 is provided at a prescribed angle relative to a stem reference surface 204. Preferably, the predetermined reference axis 203 is provided at a right angle relative to the stem reference surface 204.
It is necessary that light emitted from each LD chip is focused on an optical disc 23 in order to read data recorded in the optical disc 23 accurately. For that reason, a lens 22 is moved towards directions indicated by a double-head arrow in FIG. 2 so that an emitted light axis of an LD chip to be used among the plurality of LD chips passes through the center of the lens 22. However, when the emitted light axis is far away from a straight line connecting the semiconductor laser device and a region to be read on the optical disc, it becomes impossible to read data accurately. Therefore, when any one of the axes of the lights emitted from the plurality of LD chips falls outside a prescribed angular range, such an optical pickup is regarded as a defective product.
Accordingly, in order to produce high-precise optical pickups at a high yield, axes of lights emitted from a plurality of LD chips are required to stay in prescribed angular ranges. For that reason, it is firstly required that, in forming a semiconductor laser element, a plurality of LD chips are die-bonded accurately on a sub-mount and, more specifically, these LD chips are die-bonded after their positions are corrected to make their emitted light axes generally parallel each other. Further, it is required that, in manufacturing a semiconductor laser device, the semiconductor laser element accurately formed is mounted on the stem so that the emitted light axes stay in the prescribed angular ranges.
The following description discusses the conventional method and apparatus for manufacturing a semiconductor laser device by die-bonding a plurality of LD chips on one sub-mount to form a semiconductor laser element, and die-bonding said semiconductor laser element on a stem.
A. Constitution of an Apparatus for Manufacturing a Semiconductor Laser Device
The conventional apparatus for manufacturing a semiconductor laser device is described by referring to FIG. 4.
The conventional apparatus for manufacturing a semiconductor laser device 4 comprises an element sheet part 401, an intermediate stage part 402, an emitted light axis recognizing part 403, a die-bonding part 404, a contacting part 405, a transferring movable part 406, shape-recognizing cameras (407 and 408) and others.
The element sheet part 401 is a part for supplying a semiconductor laser element 1 in which one or more LD chips are die-bonded on one sub-mount in a previous process.
The intermediate stage part 402 is a part for correcting a position of the supplied semiconductor laser element 1 by shape-recognition or the like.
The emitted light axis recognizing part 403 is a part for recognizing an emission point, an emitted light axis and the like, and has only an Y-axis actuator as a mechanism for capturing the emission point and the emitted light axis.
The die-bonding part 404 is a part for die-bonding the semiconductor laser element, a position of which has been corrected, on a stem 201 of a semiconductor laser device 21.
The contacting part 405 has one contact probe pair, which is provided separately outside the transferring movable part 406, and has a YZ-axis actuator as a mechanism for making a contact.
The transferring movable part 406 has two collet parts (409 and 410) and, each has a Z-axis actuator as a mechanism for moving the collet part up and down.
B. A Method for Manufacturing a Semiconductor Laser Device
Next, the conventional method for manufacturing a semiconductor laser device will be explained below.    (1) A semiconductor laser element set in the element sheet part 401 is position-corrected by shape-recognizing with a camera 407 provided above the element sheet part 401.    (2) The transferring movable part 406 is moved right, and the collet part 409 is moved up and down above the element sheet part 401 to take up the semiconductor laser element 1, a position of which has been corrected by shape-recognizing.    (3) The transferring movable part 406 is moved left, and the collet part 409 is moved up and down above the intermediate stage part 402 to set the semiconductor laser element 1 taken up, on the intermediate stage part 402.    (4) The transferring movable part 406 is moved to awaiting position, and the part 406 is halted to shape-recognize the semiconductor laser element 1 set on the intermediate stage part 402 with the camera 408 provided above the intermediate stage part 402.    (5) During shape-recognizing the above semiconductor laser element set on the intermediate stage part 402, as in the step (1), a next semiconductor laser element 1′ set in the element sheet part 401 is shape-recognized with the camera 407 provided above the element sheet part 401.    (6) The contacting part 405 is moved to above the intermediate stage part 402 and moved down so as to contact with the semiconductor laser element 1 in order to recognize the emission point and the emitted light axis of the above semiconductor laser element 1 set on the intermediate stage part 402, which has been shape-recognized, wherein the emitted light axis is recognized only for one predetermined LD chip with the emitted light axis recognition camera 403.    (7) The contacting part 405 is moved up, the part 405 is moved out of an area above the intermediate stage part 402, the transferring movable part 406 is moved right, and the collet part 410 is moved up and down to take up the semiconductor laser element 1 on the intermediate stage part 402, for which the emission point and the emitted light axis have been recognized.    (8) During taking up the semiconductor laser element 1 on the intermediate stage part 402 as described above, as in the step (2), the collet part 409 is moved up and down above the element sheet part 401 to take up the semiconductor laser element 1′.    (9) The transferring movable part 406 is moved left and, thereafter, the collet part 410 is moved up and down above the die-bonding part 404 to die-bond the semiconductor laser element 1 taken up from the intermediate stage part 402, on the stem 201.    (10) During die-bonding the semiconductor laser element taken up from the intermediate stage part 402, on the stem 201, as in the step (3), the semiconductor laser element 1′ taken up from the element sheet part 401 is set on the intermediate part 402.
By repeating the above steps, semiconductor laser devices are manufactured.
As described above, according to the conventional method, even when a semiconductor laser element comprises a plurality of LD chips, an emitted light axis of only one representative LD chip is recognized with an emitted light axis recognizing part and, based on the result, a position of the semiconductor laser element is corrected to die-bond on a stem.
In the conventional method in which a semiconductor laser element with a plurality of LD chips die-bonded on one sub-mount is die-bonded on a stem of the semiconductor laser device, when the contacting part 405 is provided separately outside the transferring movable part 406, in order to recognizing an emitted light axis of a semiconductor laser element, it must be confirmed that the collet part 409 of the transferring movable part 406 has been moved out of an area above the intermediate stage part 402 and, thereafter, the contacting part 405 is moved to above the intermediate stage part 402, and the part 405 is moved down so as to contact with the semiconductor laser element.
In addition, in taking up the semiconductor laser element, for which the emitted light axis has been recognized, it must be confirmed that the contacting part 405 is moved out of an area above the intermediate stage part 402 and, thereafter, the collet part 410 on the transferring movable part 406 is moved to above the intermediate stage part 402.
Moreover, since the contacting part 405 is provided separately outside the transferring movable part 406, actuators specially for moving the contacting part 405 to above the intermediate stage part 402 and for moving up and down so as to contact with the semiconductor laser element, are necessary.
When actuators for moving collets of the collet parts (409 and 410) on the transferring movable part 406 up and down and for moving the contacting part 405 up and down are provided on the transferring movable part 406 and moved together, a transferring load increases as compared with a case where such actuators are provided separately outside the transferring movable part, and the transferring movable part 406 cannot be moved quickly to that extent.
In order to conduct shape-recognition with the camera 408 above the intermediate stage parts 402, in view of the size and arrangement of the collet parts (409 and 410) on the transferring movable part 406, the transferring movable part 406 must be temporally moved to a waiting position (where an image of the element on the intermediate stage part 402 can be taken with the camera 408), and the shape of the semiconductor laser element must be taken and treated in a state that the part 406 is halted.
In addition, according to the conventional method for manufacturing a semiconductor laser device, only one contact probe pair is provided regardless of the number of LD chips in the semiconductor laser element, an emitted light axis is recognized only for one predetermined LD chip, and the semiconductor laser element is die-bonded on a stem using the above result. Therefore, in a case where emitted light axes from two LD chips are generally parallel as shown in FIGS. 12(a) and 12(b), these emitted light axes from the two LD chips may stay in an acceptable range (see FIGS. 13(a) and 13(b)), but, on the other hand, in a case where the directions of the light axes of the two LD chips differ each other, even when the light axis of one LD chip can stay in the acceptable range, the light axis of the other LD chip lies around the limit of the range or outside the range (see FIGS. 13(c) and 13(d)). Thus, it is difficult to make all the light axes stay fully in prescribed angular ranges, leading to a high percentage of defective semiconductor laser devices.